m4: Check for rl_completion_quote_character
Apparently we can't assume that people run readline recent enough
to have rl_completion_quote_character (added in readline-5.0
released in 2011). However, we can't compile without it. So if
not present, disable readline.
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Andrea Bolognani <abologna@redhat.com>